Benzaldehyde has been shown to have anti-tumor activity. See Kochi, M. et al, "Anti-Tumor Activity of Benzaldehyde," Cancer Treat. Rep., 64(1) 21-3, January 1980. It is theorized that benzaldehyde has such anti-tumor activity because it acts very strongly and immediately with cysteine. Since fast growing cells require more cysteine than normal cells, treatment with benzaldehyde will theoretically interfere with fast multiplication of tumor cells without being unduly threatening to normal cells. Also, leucotriene-D.sub.4, which is essential for cell multiplication, is a conjugate of arachidonic acid with cysteine. It is believed that by depriving the body of cysteine, multiplication of new cells is suppressed.
Other aldehydes, much as salicylaldehyde, formaldehyde, glutaraldehyde, and others, also have caustic and cytotoxic properties.
Penicillamine (dimethylcysteine) has known therapeutic utility. One property of penicillamine is its ability to form complexes with copper and remove it from the body. Thus, penicillamine is commonly used for the treatment of diseases caused by excess copper, e.g., Wilson's Disease.
Some tumors are known to show high tyrosinase activity. Tyrosinase is a metallo enzyme and requires copper. Tyrosinase can thus be inhibited by removing copper.